The official KCNA news agency has lauded Kim Jong Un as "the great successor" and "the outstanding leader of our party, army, and people," after the announcement that his father had died on December 17.

But there are questions over how much authority the younger Kim has, since he is only in his late 20s and has had little time to prepare for the role.

It's raised concerns in the West about the stability of the isolated state and whether the transition to Kim the younger will be smooth or marked by power struggles.

"We have very little to go on in terms of how much power has been transferred to the son, Kim Jong Un. We don't know, for example, how his authority is within the army or in the communist party," says Robert Ward, an expert on North Korea with the Economist Intelligence Unit in London. "And this uncertainty is one of the things that's driving the concerns -- I suppose -- around the world at the news of Kim Jong Il's death."

Ward notes that the younger Kim is "about 27 years old, untried. The transfer of power has been going on for a couple of years now, after Kim Jong Il -- his father -- became very ill. But his young chap probably quite pampered and lacks -- in my view -- all the nous and the political wiliness, if you like, that his father had."

The Mysterious Younger Kim

Little is known about Kim Jong Un, who has stood for months at the center of speculation over who would succeed his father.

There are few photographs of the younger Kim. His mother was a dancer and Kim Jong Il's third wife, Ko Yong Hi, according to media reports.

Kim Jong Un was reportedly educated under a false name in an international school in Switzerland until 1998.

Kim Jong Un may face threats to his authority.

The Swiss weekly magazine "L'Hebdo" reported that he left the school at the age of 15 without completing his diploma. It quoted his classmates as describing him as shy and introverted and that he liked to ski and play basketball.

But the South Korean newspaper "The Korea Herald" reported that he supposedly developed an early sense of authority and power.

Since his return to Pyongyang, he is known to have attended the Kim Il Sung Military University. He emerged in 2009 as his father's likely successor.

Last year, he was made a four-star general and given senior ruling party posts, despite his lack of any military experience.

Consolidating Power

The appointment occurred before the largest meeting in 30 years of the ruling communist party, the Workers Party of Korea, in September 2010.

During the previous meeting in 1980, Kim Jong Il was anointed his own father's political heir, eventually taking over the country after Kim Il Sung died in 1994.

"This past year has been a period in which Kim Jong Il helped his son consolidate his power at maximum speed," says Haksoon Paik, director for the Center of North Korean Studies at the Seoul-based private think tank Sejong Institute. "One critical factor is whether or not there's an alternative power or alternative person who can replace Kim Jong Un. There is no such figure in North Korea under the supreme-leader system."

Paik adds that "Now we see that Kim Jong Un is supported by the key members of North Korean politics as the new leader. So I think in terms of stabilization of his power there's been much achievement. There is no doubt about that."

WATCH: The official KCNA news agency has lauded Kim Jong Un as "the great successor" and "the outstanding leader of our party, army, and people." (AP video):

The sister and brother-in-law of the late Kim Jong Il are expected to play a major role in the transition of power.

Kim Jong Il's sister, Kim Kyoung Hui, was elevated to a four-star general at the same time as Kim Jong Un.

Some analysts say her husband, Jang Song Thaek, often considered North Korea's No. 2 leader, is likely to act as regent for Kim Jong Un for a while. But Ward says a power struggle is "highly likely."

"When Kim Jong Il took over in the 1990s, even then it was uncertain for a few years just how secure Kim Jong Il's grip on power was -- and his ascendancy to power followed many, many years of being trained for it," Ward says.

He notes that since the younger Kim "is so young and untried, I think there'll be a lot of people, a lot of factions within the government, within the army, within the communist party, all vying for control of this young man. The glue that holds this regime together is the Kim dynasty, and I think while you'll have this factional instability and infighting, no one would want to undermine their particular support for the North Korean regime."

Neighbors Grow Anxious

The death of North Korean leader has triggered concern among the country's neighbors, while Asian stock markets fell after the announcement.

A South Korean protester expresses his opposition to North Korea's Kim dynasty.

South Korea, which remains technically at war with the North, urged people to "go about their usual economic activities," while putting its military on alert. Japan's government convened a special security meeting.

However, China, North Korea's closest ally and biggest trading partner, expressed "distress" at the news of his death.

Ward says Kim's death could herald unstable times in North Korea, saying the country might act provocatively to divert attention away from domestic instability.

"This is what they do. They have very little to bargain with, but one of the things they do have that terrifies everybody is nuclear capabilities, large army, chemical weapons, and so on. So they flex these muscles whenever things go wrong, whenever they need to be noticed by the world," Ward says.

"And given how uncertain Kim Jong Un's grip on power is, there is a risk, of course, that he may decide to show his military credentials, if you like, by launching maybe another nuclear test, or maybe another attack on something, or a missile launch for domestic display."

Unconfirmed South Korean reports say the North tested a short-range missile off the eastern coast of the nuclear-armed nation on December 19, but it was not clear if the test was connected to the announcement of Kim Jong Il's death.

North Korea conducted its first nuclear tests in 2006, followed by a second one three years later. Multinational talks aimed at disarming Pyongyang involving the United States, China, South Korea, Japan, Russia, and North Korea have been deadlocked for months.